Multi-standard transmitter system and method for a wireless communication system

Abstract

A transmitter 108 converts a digital baseband signal input 150 for transmission by an antenna 114 to support multiple communication standards. An over-deviation phase multiplier 130 increases signal phase deviation by a factor of M. A digital phase modulator 176 applies trigonometric lookup tables. A digital intermediate frequency up-converter 132 up-shifts frequencies of desired signal content. First and second digital-to-analog converters (DACs) 134 and 136 use relatively low-bit operations, which add DAC noise 212. First and second low pass filters 138 and 140 apply rejection above frequencies of desired signal content. An analog I/Q modulator 142 converts from complex to real signals, adding an unwanted signal spaced from the desired signal content by an intermediate frequency multiple. A limiter 144 reduces amplitude modulated noise. An over-deviation phase divider 146 divides signal phase deviation by 1/M to reduce phase modulated noise.

Description

BACKGROUND OF THE INVENTION1. Technical FieldThe present invention relates generally to wireless communication systems and, more particularly, to a multi-standard transmitter system and method for noise reduction through phase modulation.2. Description of Related ArtWireless communication devices, such as cellular telephones, are widely used as a replacement for conventional telephone systems. One advantage of the wireless communication devices is their portability. The user can operate the wireless communication devices from virtually any point on earth. Since component size, weight, and power requirements of the wireless communication device can detrimentally affect portability, they are important factors that directly impact its utility.For communication to occur, signals are transmitted from and received by components of the wireless communication devices. Transmitters, either separate or part of a transceiver, handle transmission tasks for the wireless communication device. Tra...

AI Technical Summary

Benefits of technology

Other aspects include a limiter configured to amplitude limit a limiter input signal and thereby reduce an amplitude modulated noise component of the real analog signal. An over-deviation phase divider is configured to divide the phase deviation of an over-deviation input signal by a division factor of M to reduce remaining portions of the DAC noise and to reduce the unwanted signal. The over-deviation phase divider is further configured to bandpass the over-deviation input signal to further reduce the unwanted signal and thereby output a phase conditioned analog signal including reduced DAC noise and reduced unwanted signal. The phase conditioned analog signal has a phase deviation that is substantially 1 / M of the phase deviation of the real analog signal, the combined power levels of the remaining DAC noise and the unwanted signal after processing are insufficient to violate the noise requirement of the first communication standard.

Problems solved by technology

Since component size, weight, and power requirements of the wireless communication device can detrimentally affect portability, they are important factors that directly impact its utility.

Digital-to-analog conversion is an important aspect for transmitters since it has the potential of producing a great deal of signal noise.

Other conventional approaches use DACs with fewer number of operational bits to reduce costs, but are forced to alleviate the additional noise caused by the lower bit DACs by using elaborate filtering.

The trade-off analysis between the amount of noise generated by low-bit DACs versus the expense associated with high-bit DACs become even more complex for transmitters configured for a multi-standard communication device such as a multi-standard cellular telephone.

In this case, for GSM, if an 8-bit or 9-bit DAC were to be used, even more extensive and elaborate filtering would be required.

Conventional approaches that address use of cellular telephones with more than one communication standard, such as with GSM and WCDMA, struggle with the challenge of meeting the noise requirements of both standards as it relates to digital-to-analog conversion of signals internal to the cellular telephone.

Unfortunately, the conventional approaches have been relatively expensive and complicated to implement.

Images